Ionic liquid as a novel surface passivation for InAs/InAsSb type-II superlattice infrared detector

This research paper reports a novel approach to the passivation of InAs/InAsSb type-II superlattice mesa structures, using a hydrophobic ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [hmim][NTf2]. The most important advantages of ionic liquids are low vapor pressure, chemical resistance in a wide temperature range, and a simple procedure of applying to semiconductor structures. In the proposed technology, the ionic liquid is directly applied to a detector mesa after the metallization process. The measurements of dark current density–voltage characteristics of detector mesa structures reveal that the [hmim][NTf2] ionic liquid serves as passivator. The dark current density after passivation decreases and does not increase even after accelerated aging performed by heating samples for 24 h at 80 °C in air. Scanning electron microscope imaging, in turn, reveals that the hydrophobic ionic liquid forms a thin layer of several dozen nanometers on the surface of the detector mesa and does not cause short circuits. The ionic liquid also protects the device against atmospheric conditions; therefore, there is no need to create an encapsulating layer additionally protecting the slope of the detector mesa.